Disk drives are commonly used to store large amounts of data in a readily available form. Typically, the primary components of a disk drive are a head disk assembly and a printed circuit board assembly (PCBA) which, when fixed to one another, form a functional unit that is then connected to a computer. The head disk assembly includes an actuator having a voice coil motor (VCM), a head mounted on the actuator, at least one data storage disk mounted on a spindle motor for rotating the storage disk near the head and a servo control system for moving the actuator to position the head over a desired track so that read/write operations may be performed on the disk.
A widely used measure of performance of a disk drive is the number of I/O operations performed by the disk drive. The quickness of the I/O operations are in turn affected by the seek time of the disk drive which is the time required by the actuator to reposition the head over a desired track. A disk drive having a short seek time will generally be able to access a requested track of data more quickly than a drive having a longer seek time. To achieve the high degrees of actuator acceleration for a quick repositioning of the head, a relatively large current is often required to flow through the VCM.
Unfortunately, when large amounts of current are directed through the VCM, the rate of heat gain caused by the finite resistance of the windings of the VCM coil may exceed the rate of heat loss to the environment. Thus, a rapid succession of seek operations may excessively raise the temperature of the coil. The excessive heat may deform the coil, and cause overmold material to delaminate from the actuator assembly, lose its rigidity and/or outgas particulates into the disk drive enclosure, with deleterious results. Thus, to prevent such damages, the VCM coil must be inhibited from overheating.
Currently, a widely used method is imposing mandatory delay time between successive seeks if the temperature of the VCM rises to above a predetermined temperature threshold. The imposed delay allows for the VCM to cool down via heat loss to the environment. While this approach can effectively prevent the VCM from overheating, the imposed delays degrades the overall seek performance of the disk drive.
Accordingly, what is needed is a reduction in the seek time penalty in the disk drive while effectively preventing the VCM from overheating.